A vision system may attempt to infer the relative position of a vehicle with respect to harvested crop (e.g., hay) lying on the ground in a field. However, background art vision systems may require excessive computational resources or tend to respond too slowly for real-time navigation of a vehicle. Further, vision systems may be inaccurate because of variations or discontinuities in the windrows, harvested crop rows, or generally rectangular piles of clippings lying in the field. Therefore, a need exists for a robust vision system for vehicle guidance that is less computationally demanding, more responsive, and more resistant to guidance errors associated with variations in the windrows, harvested crop rows, or generally rectangular piles of clippings lying in the field.